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Evaluating climate signal recorded in tree-ring δ¹³C and δ¹⁸O values from bulk wood and α-cellulose for six species across four sites in the northeastern UShttps://ddd.uab.cat/record/186835
Rationale : we evaluated the applicability of tree-ring δ¹³C and δ¹⁸O values in bulk wood – instead of the more time and lab-consuming α-cellulose δ¹³C and δ¹⁸O values, to assess climate and physiological signals across multiple sites and for six tree species along a latitudinal gradient (35°97'N to 45°20'N) of the northeastern United States. -Methods: wood cores (n = 4 per tree) were sampled from ten trees per species. Cores were cross-dated within and across trees at each site, and for the last 30 years. Seven years, including the driest on record, were selected for this study. The δ¹³C and δ¹⁸O values were measured on two of the ten trees from the bulk wood and the α-cellulose. The offsets between materials in δ¹³C and δ¹⁸O values were assessed. Correlation and multiple regression analyses were used to evaluate the strength of the climate signal across sites. Finally the relationship between δ¹³C and δ¹⁸O values in bulk wood vs α-cellulose was analyzed to assess the consistency of the interpretation, in terms of CO2 assimilation and stomatal conductance, from both materials. - Results: we found offsets of 1. 1‰ and 5. 6‰ between bulk and α-cellulose for δ¹³C and δ¹⁸O values, respectively, consistent with offset values reported in the literature. Bulk wood showed similar or stronger correlations to climate parameters than α-cellulose for the investigated sites. In particular, temperature and vapor pressure deficit and standard precipitation-evaporation index (SPEI) were the most visible climate signals recorded in δ¹³C and δ¹⁸O values, respectively. For most of the species, there was no relationship between δ13C and δ18O values, regardless of the wood material considered. - conclusions: extraction of α-cellulose was not necessary to detect climate signals in tree rings across the four investigated sites. Furthermore, the physiological information inferred from the dual isotope approach was similar for most of the species regardless of the material considered. Guerrieri, RossellaThu, 15 Feb 2018 14:53:31 GMThttps://ddd.uab.cat/record/1868352017Impacts of global change on Mediterranean forests and their serviceshttps://ddd.uab.cat/record/185591
The increase in aridity, mainly by decreases in precipitation but also by higher temperatures, is likely the main threat to the diversity and survival of Mediterranean forests. Changes in land use, including the abandonment of extensive crop activities, mainly in mountains and remote areas, and the increases in human settlements and demand for more resources with the resulting fragmentation of the landscape, hinder the establishment of appropriate management tools to protect Mediterranean forests and their provision of services and biodiversity. Experiments and observations indicate that if changes in climate, land use and other components of global change, such as pollution and overexploitation of resources, continue, the resilience of many forests will likely be exceeded, altering their structure and function and changing, mostly decreasing, their capacity to continue to provide their current services. A consistent assessment of the impacts of the changes, however,remains elusive due to the difficulty of obtaining simultaneous and complete data for all scales of the impacts in the same forests, areas and regions. We review the impacts of climate change and other components of global change and their interactions on the terrestrial forests of Mediterranean regions, with special attention to their impacts on ecosystem services. Management tools for counteracting the negative effects of global change on Mediterranean ecosystem- services are finally discussed. Peñuelas, JosepWed, 31 Jan 2018 16:03:24 GMThttps://ddd.uab.cat/record/1855912017Leaf-level photosynthetic capacity in lowland Amazonian and high-1 elevation, Andean tropical moist forests of Peruhttps://ddd.uab.cat/record/180483
We examined whether variations in photosynthetic capacity are linked to variations in the environment and/or associated leaf traits for tropical moist forests (TMFs) in the Andes/western Amazon regions of Peru. We compared photosynthetic capacity (maximal rate of carboxylation of Rubisco (Vcmax), and the maximum rate of electron transport (Jmax)), leaf mass, nitrogen (N) and phosphorus (P) per unit leaf area (Ma, Na and Pa, respectively), and chlorophyll from 210 species at 18 field sites along a 3300-m elevation gradient. Western blots were used to quantify the abundance of the CO2-fixing enzyme Rubisco. Area- and N-based rates of photosynthetic capacity at 25°C were higher in upland than lowland TMFs, underpinned by greater investment of N in photosynthesis in high-elevation trees. Soil [P] and leaf Pa were key explanatory factors for models of area-based Vcmax and Jmax but did not account for variations in photosynthetic N-use efficiency. At any given Na and Pa, the fraction of N allocated to photosynthesis was higher in upland than lowland species. For a small subset of lowland TMF trees examined, a substantial fraction of Rubisco was inactive. These results highlight the importance of soil- and leaf-P in defining the photosynthetic capacity of TMFs, with variations in N allocation and Rubisco activation state further influencing photosynthetic rates and N-use efficiency of these critically important forests. Bahar, Nur H.A.Wed, 06 Sep 2017 09:08:12 GMThttps://ddd.uab.cat/record/1804832017